Continued effort will be made to identify differentiation block of leukemic B cells. Various human T cell subpopulations will be identified with heteroantisera. The role of these T cell subpopulations in the induction of B cell differentiation to plasma cells will be determined. A subpopulation of B cells with different sg isotypes will be isolated from tonsillar and peripheral blood and will be subjected to differentiation induction to determine their capability in the expression of g isotypes intracellularly.